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1. Field of the Invention
This invention relates to piping that connects a steam boiler to piping that carries water from condensed steam back to the boiler.
2. Description of Related Art
Steam boilers used to be connected a steam outlet pipe from the upper part of the boiler and a separate condensate return pipe at the lower part of the boiler as shown in FIG. 1. Steam left the boiler through steam outlet piping and returned through the condensate pipe. While this system worked it had two major disadvantages.
The first disadvantage is that if a condensate return pipe leaked the loss of water could lower the boiler""s water level enough to damage the boiler from overheating as a result of firing without enough water in it. Second, there was no way to prevent water from sloshing back and forth between the boiler and the condensate return piping in response to small and constant pressure fluctuations resulting from the bubbling of water boiling, unsteady flow of air, water, and steam in the system piping, and opening and closing of any valves that might be in the system. This sloshing around makes control of the boiler water level by [an] automatic device difficult because the water level control apparatus is confused by the fluctuating water level.
One solution used was to install a check valve in the return pipe. A check valve is a device that has a moving doorlike flapper that is intended to be opened by flow in one direction and closed by flow in the other direction. The check valve protected the boiler from a sudden loss of water out a leaking condensate return pipe, and prevented the sloshing back and forth by permitting water to flow only one way in the condensate return pipe: toward the boiler. Unfortunately, check valves are unreliable. They can clog with dirt, sticking open or closed. This makes their use impractical.
The next system that became common is the Hartford Loop as shown in FIG. 2. The Hartford Loop is said to be named after one or more of the insurance companies in Hartford, Conn. that refused to insure a steam boiler installed without a Hartford Loop. It is installed by piping the condensate return pipe into the equalizer pipe about 2 to 4 inches below the boiler""s water level as shown in FIG. 2.
The Hartford loop has the advantage of preventing sudden loss of large amounts of water caused by a pipe leak because gravity can""t drain water uphill out the condensate return pipe. The water loss is limited to 2 to 4 inches below the boiler""s water level because that is where the condensate return pipe connects to the equalizer pipe. A loss of 2 to 4 inches is generally allowable and won""t damage a typical steam boiler. Steam pressure inside the boiler is prevented from forcing the water up and out the return pipe by the equalizer pipe which exerts equal pressure on the top of the condensate return piping. This is all accomplished without any moving parts or restricted areas in the piping that would be prone to clogging, thus it is very reliable. Unfortunately, the Hartford Loop has the disadvantage of not solving the problem of water sloshing around between the steam boiler and the condensate return piping. Despite this drawback the safety and reliability of the Hartford Loop has caused it to come into widespread use. The sloshing around problem has become accepted as normal despite the difficulty associated with use of automatic water level control apparatus on a boiler where the water sloshes around.
The present invention comprises a condensate return pipe connected to the equalizer pipe above the boiler""s water level.